当前位置:首页 > 生物研究 > 生态学 > 正文

变化迅速的生态系统影响早期人类的进化

变化迅速的生态系统影响早期人类的进化

两项发表在近期《PANS》上的研究发现,非洲奥杜威山谷(olduvai valley)周围的地形在干旱、辽阔的草原和封闭、潮湿的森林之间迅速波动,很可能影响了早期人类的进化。地方气候和植被为理解现代人类如何进化提供了一个背景,但是基于陆地的替代记录迄今为止太少,因此无法揭示出地方生态系统的定义性特征。

研究人员保存在奥杜威山谷(olduvai valley)的湖沉积物中的有机物质的碳同位素特征发现了大约200万年前哪些植物支配着当地环境,而就在那个时候直立人(Homo erectus)出现并开始扩散。研究发现,植物生命的历史揭示出了仅仅在几百年到几千年时间里开放草原突然转变成封闭森林的重复出现的模式,这与人们长期所持的一种观念相冲突,这种长期的观念认为干旱逐渐的增加促进了非洲大陆草原的扩展,而这反过来又驱动着人类进化的变化。科学家根据附近湖沉积物中的植物蜡和海藻脂的氢同位素比率构造出了奥杜威山谷(olduvai valley)生态系统的湖蒸发和降水可利用度的一个高分辨率记录。这表明该地区曾遇到了干旱的明显波动,在干旱的时期草原是主流,而在湿润的时期的特征是树木覆盖的扩展。

这些研究表明保存在湖沉积物中的有机物可以带来地方生态变化的详细历史并且揭示出过去的气候变化是如何影响人类进化的。

了解更多:

Water, plants, and early human habitats in eastern Africa

doi: 10.1073/pnas.1209405109 

Water and its influence on plants likely exerted strong adaptive pressures in human evolution. Understanding relationships among water, plants, and early humans is limited both by incomplete terrestrial records of environmental change and by indirect proxy data for water availability. Here we present a continuous record of stable hydrogen-isotope compositions (expressed as δD values) for lipid biomarkers preserved in lake sediments from an early Pleistocene archaeological site in eastern Africa—Olduvai Gorge. We convert sedimentary leaf- and algal-lipid δD values into estimates for ancient source-water δD values by accounting for biochemical, physiological, and environmental influences on isotopic fractionation via published water–lipid enrichment factors for living plants, algae, and recent sediments. Reconstructed precipitation and lake-water δD values, respectively, are consistent with modern isotopic hydrology and reveal that dramatic fluctuations in water availability accompanied ecosystem changes. Drier conditions, indicated by less negative δD values, occur in association with stable carbon-isotopic evidence for open, C4-dominated grassland ecosystems. Wetter conditions, indicated by lower δD values, are associated with expanded woody cover across the ancient landscape. Estimates for ancient precipitation amounts, based on reconstructed precipitation δD values, range between approximately 250 and 700 mm·y−1 and are consistent with modern precipitation data for eastern Africa. We conclude that freshwater availability exerted a substantial influence on eastern African ecosystems and, by extension, was central to early human proliferation during periods of rapid climate change.

Ecosystem variability and early human habitats in eastern Africa

doi: 10.1073/pnas.1206276110

The role of savannas during the course of early human evolution has been debated for nearly a century, in part because of difficulties in characterizing local ecosystems from fossil and sediment records. Here, we present high-resolution lipid biomarker and isotopic signatures for organic matter preserved in lake sediments at Olduvai Gorge during a key juncture in human evolution about 2.0 Ma—the emergence and dispersal of Homo erectus (sensu lato). Using published data for modern plants and soils, we construct a framework for ecological interpretations of stable carbon-isotope compositions (expressed as δ13C values) of lipid biomarkers from ancient plants. Within this framework, δ13C values for sedimentary leaf lipids and total organic carbon from Olduvai Gorge indicate recurrent ecosystem variations, where open C4 grasslands abruptly transitioned to closed C3 forests within several hundreds to thousands of years. Carbon-isotopic signatures correlate most strongly with Earth’s orbital geometry (precession), and tropical sea-surface temperatures are significant secondary predictors in partial regression analyses. The scale and pace of repeated ecosystem variations at Olduvai Gorge contrast with long-held views of directional or stepwise aridification and grassland expansion in eastern Africa during the early Pleistocene and provide a local perspective on environmental hypotheses of human evolution.


阅读次数:  
更多 相关资讯:
    无相关信息

发表评论